CHAPTER XX.
DIFFERENT KINDS OF PIG IRON USED
AND DEFINITION OF BRAND AND
GRADE.
The brand of an Iron refers to some characteristics peculiar to itself or distinct from what can be found in some other irons; as, for example, in the difference found between charcoal and coke iron, and often made by the use of different ores and fluxes, although the same fuel may be used.
The grade of an iron refers to the different degrees of hardness, strength, or contraction and chill which may be obtained from any special brand of iron. In a general way high silicon or soft irons are called high grade irons, and low silicon or hard irons low grades. It has been claimed that the amount of silicon in pig iron, and which element chiefly regulates the grade, could be told by the contraction of test bars. This is impractical. The only sensible way to define the silicon or any other metalloid contents of any test bar or casting is by chemical analysis. The contraction merely assists in defining the grade of iron and nothing more.
Grading pig iron should mean sorting it into cars or piles, according to the degree of strength or hardness thought obtainable from it when re-melted to make castings. A few years back every furnace had its " graders/* whose special business it was to separatetors which strongly recommend the use of sandless pig iron. For methods of calculating percentages of silicon, sulphur, etc., as found in iron, to obtain averages for making mixtures, see Chapter XXXVI.